1. Field of the Invention
Aspects of the present invention relate to a method and apparatus for forming an image, and more particularly, to a multi-pass image forming apparatus and a method for forming an image when mis-pick up occurs in the multi-pass image forming apparatus.
2. Description of the Related Art
In general, a color image forming apparatus receives a digital image signal corresponding to a desired image, forms an electrostatic latent image on a photosensitive medium using an exposure unit (such as a laser scanning unit (LSU)), develops the electrostatic latent image using a developer in order to develop printing data, transfers the electrostatic image to printing paper, and fuses the electrostatic image on the printing paper by applying heat and pressure thereto to form a desired color image. The color image forming apparatus uses yellow (Y), magenta (M), cyan (C), and black (K) toners. Thus, the color image forming apparatus requires four developers in order to apply the four toners to the photosensitive medium as the electrostatic latent image.
Color image forming apparatuses may be classified into a single-pass image forming apparatus and a multi-pass image forming apparatus. The single-pass color image forming apparatus includes four exposure units and four photosensitive media, and the multi-pass color image forming apparatus generally includes a single exposure unit and a single photosensitive medium. The single-pass color image forming apparatus is widely used to print images at high speed, i.e., the single-pass color image forming apparatus prints a color image as quickly as a black-and-white image. However, the single-pass color image forming apparatus requires four exposure units and four photosensitive media, and thus the single-pass color image forming apparatus is expensive and not suitable for miniaturization.
In the case of the multi-pass color image forming apparatus, the exposure, developing, and transfer processes are repetitively performed for respective colors to form color images. The formed color images are superposed on an intermediate transfer belt (ITB), so that color printing data are developed, transferred, and fused to printing paper.
FIG. 1 is a view showing the construction of a conventional multi-pass image forming apparatus. Referring to FIG. 1, the conventional multi-pass image forming apparatus includes an electrification roller 110, a developing roller 120, an exposure unit 130, an organic photo conductor (OPC) drum 140, a first transfer roller 150, a second transfer roller 153, an Intermediate Transfer Belt (ITB) 156, driving rollers 159, a pick up solenoid 160, a pick up roller 163, a cassette 166, a registration solenoid 170, a registration roller 173, a registration sensor 176, a fusing roller 180, an output roller 190, and an output sensor 193.
A process of forming an image using the above-described multi-pass image forming apparatus will now be described. The electrification roller 110 rotates in contact with or out of contact with an outer surface of the OPC drum 140 to supply electric charges to the OPC drum 140 and electrifies the outer surface of the OPC drum 140 to a uniform electric potential. The exposure unit 130 irradiates light corresponding to image information on the electrified OPC drum 140 and forms an electrostatic latent image. Generally, the exposure unit 130 may be an LSU using a laser diode (LD) as a light source. The developing roller 120 supplies a toner to the OPC drum 140 to develop printing data. In order to transfer the printing data developed on the OPC drum 140 to the ITB 156, a first bias voltage is applied to the first transfer roller 150. The ITB 156 is driven by the driving rollers 159. The second transfer roller 153 is installed opposite to the ITB 156. The second transfer roller 153 is spaced apart from the ITB 156 during the transfer of the printing data from the OPC drum 140 to the ITB 156, and comes into contact with the ITB 156 under a predetermined pressure when the printing data is completely transferred to the ITB 156.
Meanwhile, printing paper to which the printing data is to be transferred passes between the ITB 156 and the second transfer roller 153 and is picked up as follows. When a predetermined voltage is applied to the pick up solenoid 160, the pick up roller 163 picks up the printing paper from the cassette 166 in which the printing paper is stored. When the registration roller 173 is driven by the registration solenoid 170, the printing paper that is picked up by the pick up roller 163 is conveyed to the second transfer roller 153. The registration sensor 173 senses a front end of the picked-up printing paper to confirm that the printing paper is normally picked up by the pick up roller 163, and aligns the printing paper. The printing data transferred from the ITB 156 is transferred to the printing paper that is conveyed to the second transfer roller 153. The printing paper to which the printing data is transferred is fixed by the fusing roller 180 and output via the output roller 190. The output sensor 193 senses the printing paper and confirms that the printing paper is output.
When forming a mono-color or multi-color image using the multi-pass image forming apparatus, the apparatus outputs an error message even in the case of only one mis-pick up. As a result, even if only one mis-pick up occurs due to for example, a mechanical slip, the apparatus directly outputs an error message and the frequency of errors increases. Also, when forming an image using the multi-pass image forming apparatus, a process of picking up printing paper is performed separately from a process of transferring printing data to the ITB. Thus, even if mis-pick up occurs, the printing data is already transferred to the ITB, thereby wasting toner.